The present invention relates to a kind of composite metal coil or plate and its manufacturing method.
Composite metal plates, such as those consisting of plain carbon steel plates composed or clad with stainless steel plates, copper plates or titanium plates, have been widely used. Composite metal plates are used mainly because they are economical, resource-saving and can be used as special materials for equipment. For example, a stainless steel plate is more suitable for manufacturing anti-corrosive pressure vessels, but it costs too much. If a composite metal plate made of plain carbon steel plate and a stainless steel plate is used to make the same pressure vessels, the stainless steel plate will only constitute 2xcx9c10% of the whole composite metal plate in thickness. Thus, the production cost is dramatically reduced while a high anti-corrosion capacity with sufficient strength is maintained. In addition, since heat-resisting, anti-corrosion and conductive materials such as copper, nickel and chromium are expensive and scarce, it will be a quite resource saving if composite metals of double or triple plates are used.
There are two main methods of manufacturing composite metal plates today: explosion cladding and hot-rolling cladding. Both methods have common as well as respective limitations.
1. Neither method is suitable for continuous production. Only single piece or unit production is possible. Hence the productivity is very low.
2. Since the size of the composite area is limited by either method, only composite materials and composite spare parts can be produced. That means higher production costs.
3. A number of factors can affect the explosion cladding. They include the type and amount of explosives used, the gap and angle between the clad plate and the parent plate, the buffer materials used, etc. As a result, yield of the finished products is very low.
When performing explosion cladding, a parent plate is placed on a flat and firm working anvil, and a clad plate is placed on the parent plate at a certain angle. After that, explosive is put on the clad plate, which explodes and gives the clad plate an extremely powerfull impact force to collide with the parent plate. The collision energy is large enough to form metallurgical combination, namely inter-atomic combination at interfaces of the two plates, thereby forming a composite material with a certain degree of shearing strength. The advantage of explosion cladding is that it can produce composite materials in various shapes, such as clad slabs, clad capped ends, clad pipes, etc.
Hot-rolling cladding is to properly flatten by machines the cladding surfaces of the parent plate and the clad plate, keep those surfaces clean, then place the surfaces of the two plats face to face, and superimpose those with periphery welded and vacuumized. After that, the interfaces of the plates to be clad are sealed to avoid oxidation. Thereafter, put the two superimposed plates into a heating furnace for heating (1200xc2x0 C.). After keeping the plates at a constant temporary for a certain period of time, hot-roll the plates. The rolling force (reduction force) is about several thousand tons and the reduction ratio per roll is over 45%xcx9c55%. The rolling force (reduction force) is determined by the thickness of the parent plate, the clad plate and the finished composite plate. The power of a hot-rolling mill is above ten thousand KW. Therefore, the investment and equipment manufacturing costs are very high, which increases the product prices. As a result, this method can only be used in some special sectors and is impossible to be used in civil and other common sectors. After hot rolling, the superimposed plates become the required composite material.
Japanese Patent JP58-212884 provides a method of manufacturing a narrow ( less than 300 mm in width) strip from an aluminum strip and a stainless steel strip at a low temperature with large reduction. By this method, two different materials or strips, after uncoiling, are preheated to a certain temperature (200xc2x0 C.) by heating rollers, and then are sent to a rolling mill for rolling cladding. The parent plate/strip and the clad plate/strip may be continuously clad into a composite metal plate or strip. Before the plates or strips to be clad reach the roller gap, they are heated to diffusion temperature, making diffusion occur at the roller gap or at the moment the plates or strips leave the roller gap. There is certain rolling deformation of the plates or strips during rolling cladding. By this method, composite strips with certain combined strength can be obtained. Nevertheless, this method is not perfect. Due to the preheating temperature, only diffuision combination, instead of metallurgical combination, can be obtained by this method. Macroscopically, the surfaces to be clad look smooth after cleaning, but microscopically there are numerous concaves and convexes. In contrast with the previously mentioned hot-rolling cladding method, the latter""s heating temperature is rather low (below 300xc2x0 C.) and reduction is much smaller. Hence, many micro-areas (micro-zones) on the surfaces to be clad are not perfectly bonded or composed during cladding, and it is quite difficult for atoms to inter-diffuse. Under this condition, those micro-areas cannot be well clad, which results in unclad areas in those micro-areas (micro-zone). As a result, the composed or composite strength is poor.
The object of the present invention is to provide a high quality, well-clad composite metal coil or plate with improved combining or composite strength and without the usual unclad areas.
Another object of the present invention is to present a method of manufacturing composite metal coils or plates. This method provides better cladding, eliminates the unclad areas between the clad coil/plate and the parent coil/plate, and improves the composed or composite strength (over 280 Mpa).
The present invention provides a kind of composite metal coil or plate which includes one parent metal coil or plate, at least one clad metal coil or plate, and an interlayer composed of atoms of a brazing filler, the parent coil or plate and the clad coil or plate. The interlayer is about 2xcx9c10 xcexcm in thickness.
The present invention also provides a method of manufacturing composite metal coils or plates, which includes the following steps:
(1) Clean, polish and dry or bake the surfaces of a parent metal coil or plate and a clad metal coil or plate that are to be clad; put a brazing filler foil between the said surfaces to be clad and superimpose the parent and clad metal coils or plates;
(2) Put the said superimposed parent and clad metal coils or plates as well as the brazing filler foil specified in step (1) into protective inert or reductive atmosphere at 850-1000xc2x0 C. for pre-cladding;
(3) After pre-cladding, hot-rolling clad the superimposed metal coils or plates at 900-1050xc2x0 C. in an inert or reductive atmosphere. A composite metal coil or plate is obtained after cooling.